Most people can quite easily say no to a potato salad or a bowl of borscht when they aren’t hungry, but offer them fries or a cookie and they’ll often indulge even on a full belly. According to new research, this weakness for unnecessary treats comes down to the fact that our drive to satisfy our hunger and our desire for fatty foods are regulated by separate brain circuits.
Normal eating, also known as homeostatic feeding, is driven by hunger, and the motivation to continue dining is extinguished when the brain recognizes that energy levels have been replenished. However, hedonic feeding, which refers to the tendency to eat delicious foods for pleasure, can often continue even in the absence of hunger.
The new study, which appears in the journal Neuron, reveals that hedonic feeding is largely regulated by a signaling protein called nociceptin, which activates neural communication in certain key regions of the mammalian brain. This may explain why humans, dogs, and cats tend to get tubby but you never see an overweight lizard or a portly stingray.
Researchers genetically modified mice to produce fluorescent nociceptin, enabling them to track its movement through the brain. They then fed the mice with regular chow, before placing the satiated rodents in a cage containing delicious fatty foods. Despite not being hungry, the animals gleefully guzzled the calorific treats, eventually becoming overweight as a result of repeated gorging sessions.
The study authors found that when the mice were bingeing, nociceptin signaling increased in a particular brain circuit that emanated from the central amygdala, which is normally associated with emotional processing in mammals. However, chemically deactivating the neurons within the central amygdala that produce nociceptin caused the mice to stop gobbling up excess treats, but had no impact on their appetite for regular chow.
These results would seem to indicate that this particular brain circuit is responsible for promoting binge-eating, but is not involved in normal homeostatic feeding. According to the researchers, this neural pathway likely evolved in mammals that typically had to survive regular famines, and therefore developed a tendency to consume as many high-calorie foods as possible even when not hungry, to provide an energy reserve.
Yet times have changed – at least for humans – and the constant availability of fatty foods means that we now have to watch what we eat. Unfortunately, though, our brains appear to be wired for bingeing, which is why we are now seeing such high rates of obesity.
This delicious dilemma faced by modern humans was summed up by study author Thomas Kash, who said in a statement that “there's just so much calorically dense food available all the time now, and we haven't yet lost this wiring that influences us to eat as much food as possible.”